Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $68.77   9.448%   $75.2674   $75.27   $75.25   $75.30  
  Purchase #2 $215.25   12.212%   $241.5363   $241.54   $241.55   $241.50  
  Purchase #3 $224.59   12.334%   $252.2909   $252.29   $252.30   $252.30  
  Purchase #4 $97.59   4.700%   $102.1767   $102.18   $102.20   $102.20  
  Purchase #5 $151.39   12.147%   $169.7793   $169.78   $169.80   $169.80  
  Purchase #6 $51.34   8.348%   $55.6259   $55.63   $55.65   $55.60  
  Purchase #7 $110.98   11.562%   $123.8115   $123.81   $123.80   $123.80  
  7 purchase totals = $919.91       $1,020.4880   $1,020.50   $1,020.55   $1,020.50